function splitThree(num){
    let res=String(num).split(".")
    let a=res[0]
    
     a=Number(a).toLocaleString()
    while(a.length%4!=3){a=0+a}
    let c=res[1]
    let f=""
    while(c.length>=3){
        f=c.substr(0,3)
        f=f+','
        c=c.substr(3)
    }
    res=(a+'.'+f+c)
    return res
}

splitThree(23323.3434)
console.log(splitThree(23323.3434))